Implantable medical device with flexible interconnect

ABSTRACT

An implantable medical device includes at least one receptacle configured for receiving at least one electrical lead, a printed wiring board including a processor, a flexible interconnect coupled between the at least one receptacle and the printed wiring board, and a housing forming a substantially sealed enclosure for the printed wiring board and the flexible interconnect.

This application is a continuation application of U.S. patentapplication Ser. No. 11/413,618, filed Apr. 28, 2006, the entirecontents of which are incorporated by reference herein.

TECHNICAL FIELD

The invention relates to medical devices, and more particularly, toimplantable medical devices that deliver therapy to and/or monitor apatient.

BACKGROUND

Depending on the application for which they are implanted in a patient,implantable medical devices (IMDs) may include a variety of electricaland/or mechanical components. Typically, an IMD includes a rigid housingthat houses all of its components, which are generally fragile, toprotect the components from forces to which they would otherwise beexposed when implanted within the human body. In order to avoidpotentially harmful interactions between the components and bodilyfluids, e.g., corrosion, IMD housings are typically hermetically sealed.Many IMD housings are fabricated from Titanium because of its desirablerigidity and biocompatibility.

The size and shape of an IMD housing is typically dependent on the sizesand shapes of the components of the IMD. Components common to most IMDsinclude a battery, a telemetry coil, and a circuit board that carriesdigital circuits, e.g., integrated circuit chips and/or amicroprocessor, and analog circuit components. The size, shape andrigidity of IMD housings limit the locations within the human body wherean IMD can be practically implanted.

Due to these limitations, an IMD is typically implanted within theabdomen, upper pectoral region, or subclavicular region of a patient.Leads or catheters must be used in order to deliver therapy or monitor aphysiological parameter at a location of the body other than where theIMD is implanted. Implantation and positioning of leads and catheterscan be difficult and time-consuming from the perspective of a surgeon,particularly where the IMD is located a significant distance from thetreatment or monitoring site. Moreover, the increased surgical time,increased surgical trauma, and increased amount of implanted materialassociated with the use of leads and catheters can increase the risk tothe patient of complications associated with the implantation of an IMD.

For example, IMDs that are used to treat or monitor the brain, e.g., todeliver deep brain stimulation (DBS) therapy, are implanted somedistance away from the brain, e.g., within the subclavicular region ofpatients. The long leads that connect the IMD to electrodes implantedwithin the brain require tunneling under the scalp and the skin of theneck, thereby requiring increased surgery and a prolonged amount of timeunder general anesthesia during the implant procedure, as well asincreased recovery time. In some cases, tunneling the leads under thescalp and skin of the neck requires an additional surgical procedureunder general anesthesia. The lengthy tract along the leads is moresusceptible to infection, and the leads can erode the overlying scalp,forcing removal so that the scalp can heal. Further, the long leadsrunning under the scalp and through the neck are more susceptible tofracture due to torsional and other forces caused by normal head andneck movements.

SUMMARY

In general, the invention is directed to an implantable medical device(IMD) for implantation into a recess formed in a cranium of a patient.Implantation of an IMD into a cranial recess may facilitate cranialimplantation of the IMD, rather than implantation at a subclavicular orother remote location. Cranial implantation may reduce or eliminate theneed for lengthy leads or catheters, and extensive lead tunneling ofsuch leads or catheters. Implantation of an IMD within a cranial recessmay facilitate cranial implantation by reducing the profile of the IMDabove the cranium. The reduced profile may be more cosmeticallyappealing to a patient, and reduce the likelihood of skin erosion of thescalp above the implant site.

According to some embodiments, an IMD includes a housing with a topexternal surface and an adjacent second surface that is proximate to thecranium relative to the top external surface. The second surface and thetop external surface are oriented define an acute angle. For example,the IMD may include a bottom external surface with a smaller area thanthe top external surface. In such embodiments, the second surface may bea side surface that connects the top external surface to the bottomexternal surface.

The recess in the cranium may have a similar shape to that of the IMDhousing. Accordingly, a cross-sectional area at the top of the recessmay be larger than a cross-sectional area at the bottom of the recess,and larger than a cross-sectional area at the bottom of the IMD. The IMDmay be implanted within the recess by sliding it into the recess as theangled second surface directs the IMP into the proper location withinthe recess.

The IMD may more easily initially slide into the recess because of thetop of the recess is larger than the bottom of the IMD. Thesubstantially corresponding shapes of the IMD and recess may allow theIMD to be more easily positioned in a desired orientation in the recess.Furthermore, the shape of the IMD also allows the IMD to be removed fromthe recess, e.g., for replacement, without direct access to the recess.By pulling the IMD horizontally, the angled second surface interactswith a similarly angled surface of the recess to lift the IMD out of therecess.

Consequently, the shape of the IMD may facilitate implantation of theIMD into the recess, and explantation of the IMD from the recess,without accessing the recess from directly above. For example, the IMDmay be slid under the scalp of the patient from an incision in the scalpthat is remote from the cranial recess location. In some cases,preferred sites for an incision on one hand, and the recess and IMD onthe other, may be located some distance apart. This may be due to, forexample, anatomical, physiological and cosmetic considerations. An IMDthat is configured according to the invention may facilitateimplantation at a preferred location through a relatively remotelylocated incision.

Some embodiments of the invention additionally or alternatively includea connection module coupled to the top external surface of the IMD thatis configured to receive one or more leads or catheters. The connectionmodule may be configured or oriented to receive leads or catheters thatare axially oriented and advanced in a direction substantially parallelto the top surface. Locating the connection module on the top surface,rather than for example a side surface of the IMD, may facilitate properpositioning the IMD within the recess, e.g., by keeping lead or cathetermaterial that might interfere with proper positioning outside of therecess. If the connection module were located on the side or at someother location on the IMD, a surgeon might need to create, e.g., drillor route, dedicated features or paths out of the recess to facilitateproper positioning of the IMD in the recess and to direct the leads orcatheters to burr holes or the like. Additionally, locating theconnection module on the top surface may allow one or more leads orcatheters to be connected to the IMD, and the IMD to be slid under thescalp and into a recess, without the leads or catheters being damaged bythe potentially sharp edges of the recess.

In one embodiment, the invention is directed to an implantable medicaldevice configured to at least one of deliver therapy to or monitor apatient, and configured for implantation within a recess formed in acranium of the patient. The implantable medical device comprises a topexternal surface located distally relative to the brain when theimplantable medical device is implanted within the recess, and a secondexternal surface adjacent to the top external surface and locatedproximate to the brain relative to the top external surface when theimplantable medical device is implanted within the recess. The secondexternal surface and the top external surface are oriented to define anacute angle.

In another embodiment, the invention is directed to an implantablemedical device configured to at least one of deliver therapy to ormonitor a patient, and configured for implantation within a recessformed in a cranium of the patient. The implantable medical devicecomprises a top external surface located distally relative to a brain ofthe patient when the implantable medical device is implanted within therecess, a bottom external surface located proximate to the brainrelative to the top external surface when the implantable medical deviceis implanted within the recess, a side external surface adjacent to boththe top external surface and the bottom external surface, a housing thatincludes at least at least part of the top external surface, at leastpart of the side external surface, and the bottom external surface, anda connection module mounted on the part of the housing that includes atleast part of the top external surface. The side external surfaceconverges with the top external surface to define a first edge thatsubstantially circumscribes the top external surface, and the sideexternal surface and the top external surface are oriented to define anacute angle along the first edge. The connection module is configured toreceive at least one of a lead or catheter, and the implantable medicaldevice is configured to at least one of deliver therapy to or monitorthe patient via the lead or catheter.

In another embodiment, the invention is directed to a method ofmanufacturing an implantable medical configured for implantation withina recess formed in a cranium of a patient. The method comprises formingan upper assembly for the implantable medial device, the upper assemblyincluding a top external surface of the implantable medial device,wherein the top external surface is located distally relative to a brainof the patient when the implantable medical device is implanted withinthe recess, forming a lower assembly for the implantable medial device,the lower assembly including a second external surface of theimplantable medial device, wherein the second external surface islocated proximate to the brain when the implantable medical device isimplanted within the recess, and joining the upper assembly to the lowerassembly to form a substantially sealed housing for the implantablemedical device, wherein after joining the upper assembly to the lowerassembly the second external surface and the top external surface areoriented to define an acute angle.

In another embodiment, an implantable medical device configured forimplantation within a recess formed in a cranium of a patient. Theimplantable medical device comprises a housing including a top externalsurface, wherein the top external surface is located distally relativeto a brain of the patient when the implantable medical device isimplanted within the recess, and a lead connection module located on thetop external surface, the lead connection module configured to receiveat least one lead. The implantable medical device further comprisescircuitry that at least one of delivers therapy to or monitorselectrical activity within the patient via the lead, the circuitrylocated within the housing, and a flexible tape interconnect within thehousing that electrically connects the circuitry within the housing tothe lead connection module.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-1B are conceptual diagrams illustrating an implantable medicaldevice (IMD) implanted on the cranium of a patient.

FIGS. 2A-2B are conceptual diagrams illustrating a rectangularimplantable medical device implanted on the cranium of a patient.

FIGS. 3A-3C are cross-sectional diagrams illustrating n implantablemedical devices that include a housing and a member that at leastpartially encapsulates the housing.

FIGS. 4A-4D illustrate techniques for manufacturing an implantablemedical device.

FIG. 5 is a functional block diagram illustrating an example implantablemedical device.

FIGS. 6A-6D illustrate exemplary cross-section shapes of implantablemedical devices.

FIGS. 7A-7B illustrate a tool for creating a cranial recess shaped toreceive an implantable medical device.

DETAILED DESCRIPTION

FIGS. 1A-1B are conceptual diagrams illustrating an implantable medicaldevice (IMD) 10 implanted on a cranium 12 of a patient 14. FIG. 1A is afront view of patient 14 and IMD 10, while FIG. 1B is a top-down view ofpatient 14 and IMD 10. As illustrated in FIG. 1B, IMD 10 has asubstantially circular, lateral cross-sectional profile. IMD 10 includesa housing with an angled surface 11 that is proximate to cranium 12. Inthe illustrated example, angled surface 11 is a side surface of IMD 10.IMD 10 is implanted in a recess 17 formed in cranium 12.

In the illustrated example, IMD 10 includes a connection module 24,which is coupled to two electrical leads 16A and 16B (collectively“leads 16”) that extend through holes 22A and 22B (collectively “holes22”) within cranium 12, and into the brain of patient 14. In exemplaryembodiments, each of leads 16 carries a plurality of electrodes, and IMD10 delivers stimulation to and/or detects electrical activity within thebrain of patient 14 via the electrodes. IMD 10 may, for example, monitoror treat epilepsy, movement disorders, pain, or psychological disordersvia the electrodes.

Further, the invention is not limited to embodiments that include leads16. For example, in other embodiments, connection module 24 mayadditionally or alternatively receive one or more catheters in themanner described herein with respect to leads 16. In such embodiments,IMD 10 may deliver therapy to or monitor patient 14 via the catheters,e.g., delivery a drug or other therapeutic substance via the catheters.

Moreover, the invention is not limited to embodiments in which leads 16or catheters extend from IMD 10 to locations within or on the brain. Forexample, in some embodiments, leads 16 or catheters may extend tolocations proximate to cranial nerves. IMD 10 may be coupled to anynumber of leads 16 or catheters, which may extend to any position on orwithin patient 10.

The housing of IMD 10 includes angled surface 11. In the example shownin FIGS. 1A-1B, the shape of angled surface 11 substantially defines afrustum of a cone. Angled surface 11 connects a top external surface 13to a bottom external surface 19. Angled surface 11 converges with thetop external surface 13 to define an edge that substantiallycircumscribes top external surface 14. Angled surface 11 and topexternal surface 13 define an acute angle at this edge. Bottom externalsurface 19 has a smaller area than top external surface 13. Similarly,angled surface 11 and bottom external surface 19 define an obtuse anglealong the edge where bottom external surface 19 converges with angledsurface 11.

This configuration may allow the IMD 10 to be more easily and securelylocated within recess 17, which may have a substantially similar shapeto the shape of IMD 10. For example, in embodiments in which recess 17is shaped substantially similarly to the housing of IMD 10, across-sectional area at the top of the recess may be larger than across-sectional area at the bottom of the recess, and larger than across-sectional area at the bottom of the housing. As will be describedin greater detail below, IMD 10 may be implanted within the recess bysliding it into the recess as the angled second surface directs the IMPinto the proper location within the recess. The IMD may more easilyinitially slide into the recess because of the top of the recess islarger than the bottom of the IMD. Furthermore, the substantiallycorresponding shapes of the IMD and recess may allow the IMD to be moreeasily positioned in a desired orientation in the recess.

In some embodiments, connection module 24 is located on top externalsurface 13. In some embodiments, IMD 10 is implanted in recess 17 suchthat substantially the entire housing of IMD 10 located within therecess except the top surface. A physician may connect leads 16 orcatheters to connection module 24 by inserting the leads or cathetersinto the connection module in a direction that is substantially parallelto the top external surface 13. The location of connection module 24allows an implanting physician to connect leads 16 or catheters, andthen slide IMD 10 into recess 17 without worrying about the leads orcatheters being pinched or damaged by an edge of cranium 12 at recess17. The location of connection module 24 also allows any route for leads16 from IMD 10 to holes 22. Holes 22 may be any distance from IMD 10.

In order to implant IMD 10 on cranium 12 according to one exampletechnique, incision 20 is made through the scalp of patient 14, and aresulting flap of skin is pulled back to expose an area of cranium 12.The incision may, as shown in FIG. 1B, be generally shaped like a “C.”Such an incision is commonly referred to as a “C-flap” incision. Asshown in FIG. 1B, recess 17 formed within cranium 12 at a locationrelatively remote from the area exposed by incision 20.

The design of IMD 10 allows IMD 10 to be implanted within recess 17 oncranium 12 at a location remote from incision 20. The locations ofincision 20 and recess 17 are exemplary. However, the location of anincision should allow blood supply to the scalp of patient 14 andminimize damage to the nerves that innervate the scalp. Thisconsideration may conflict with other factors regarding the desiredlocation of IMD 10. For example, the thickness of cranium 12 varies.Recess 17 and IMD 10 should be located at a position on cranium 12 witha sufficient thickness to allow recess 17 to be deep enough to hold IMD10. Furthermore, another factor in selecting a location for IMD 10 isthe cosmetic appearance of IMD 10 once implanted.

Recess 17 is formed by removing bone from cranium 12. Recess 17 may beformed within a pocket beneath the scalp of patient 14 behind incision20. For example, recess 17 may be using a tool similar to that shown inFIGS. 7A-7B. The tool shown in FIGS. 7A-7B creates the circular shape ofrecess 17 that is similar to the shape of IMD 10. Other tools may alsobe used to form recess 17.

Implantation of IMD 10 may also require a physician to drill holes 22,e.g., burr holes, through cranium 12. The physician may insert leads 16or catheters through holes 22 and into the brain of patient 14. Thephysician may also place caps over holes 22 as is known in the art. Thephysician may then connect leads 16 or catheters to IMD 10, eitherdirectly or via one or more lead extensions, and places IMD 10 withinrecess 17. Angled surface 11 of IMD 10 may allow IMD 10 to slide intorecess 17 of cranium 12 without requiring further positioning. Further,the shapes of the IMD housing and recess may allow IMD 10 to beimplanted in recess 17 other than via an incision above the recess,e.g., by sliding IMD 10 under the scalp of patient 14 from a relativelyremote incision.

Once positioned as desired on cranium 12 within recess 17, IMD 10 isfairly secure because it is held within recess 17 by the scalp ofpatient 14. Optionally, IMD 10 may also be fixed to cranium 12 using anattachment mechanism such as bone screws. The skin flap may be closedover IMD 10, and the incision may be stapled or sutured. The location ofrecess 17 within cranium 12 as implanted in FIG. 1B is merely exemplary,and IMD 10 can be implanted anywhere on cranium 12.

Because IMD 10 can be implanted on cranium 12 of patient 14 rather thenmore remotely from the brain of patient 14, such as within ansubclavicular region of patient 14, the problems associated with the useof long leads or catheters needed to allow a remotely implanted IMDs toaccess the brain may be diminished or avoided. These problems includethe requirement of tunneling under the scalp and the skin of the neck,increased surgery and recovery time, an additional procedure undergeneral anesthesia, risk of infection or skin erosion along the trackthrough which the leads or catheters are tunneled, and risk of lead orcatheter fracture due to torsional and other forces caused by normalhead and neck movements.

As mentioned above, IMD 10 may deliver electrical stimulation to thebrain of patient 14 to, for example, provide deep brain stimulation(DBS) therapy, or to stimulate the cortex of the brain. Corticalstimulation may involve stimulation of the motor cortex. IMD 10 may beused to treat any nervous system disorder including, but not limited to,epilepsy, pain, psychological disorders including mood and anxietydisorders, movement disorders (MVD), such as, but not limited to,essential tremor, Parkinson's disease, and neurodegenerative disorders.

However, IMD 10 is not limited to delivery of stimulation to the brainof patient, and may be employed with leads 16 or catheters deployedanywhere in the head or neck including, for example, leads deployed onor near the surface of the skull, leads deployed beneath the skull suchas near or on the dura mater, leads placed adjacent cranial or othernerves in the neck or head, or leads placed directly on the surface ofthe brain.

IMD 10 is not limited to embodiments that deliver stimulation. Forexample, in some embodiments IMD 10 may additionally or alternativelymonitor one or more physiological parameters and/or the activity ofpatient 14, and may include sensors for these purposes. Where a therapyis delivered, IMD 10 may operate in an open loop mode (also referred toas non-responsive operation), or in a closed loop mode (also referred toas responsive). IMD 10 may also provide warnings based on themonitoring.

As discussed above, the ability of IMD 10 to be implanted close to aregion within patient 14 enables the use of shorter leads 16 orcatheters. Shorter electrical leads 16 may advantageously improve theaccuracy of such sensors by reducing noise attributable to leads 16.Shorter electrical leads 16 may also advantageously reduce the negativeaffects of imaging techniques such as magnetic resonance imaging (MRI)on a person implanted with IMD 10.

Further, as discussed above, in some embodiments IMD 10 can additionallyor alternatively deliver a drug or other therapeutic agent to patient14, such as a pharmaceutical, biological, or genetic agent. As discussedabove, connection module 24 may be coupled to one or more catheters, andIMD 10 may include a pump and related circuitry to deliver thetherapeutic agent via the catheters.

FIGS. 2A and 2B are conceptual diagrams illustrating another example IMD30 implanted within a recess 31 in cranium 12 of patient 14. IMD 30 issubstantially similar to IMD 20 of FIGS. 1A-1B except that is has arectangular, rather than circular, lateral cross-sectional shape. Forpurposes of brevity, features of IMD 30 that are common with IMD 20 arediscussed in limited detail or, in some instances, not at all. Like IMD20, the shape of IMD 30 allows for IMD 30 to be implanted within recess31 of cranium 12 at a location remote from incision 20. As was the casewith IMD 10 and recess 17, IMD 30 and recess 31 may have substantiallysimilar shapes.

In the illustrated example, as was the case with IMD 10, IMD 30 includesconnection module 24 mounted to a top external surface 34 of IMD 30.Connection module 24 may be coupled to leads 16 that extend throughholes 22 within cranium 12 and into the brain of patient 14. Forexample, each of leads may be inserted into a respective one ofreceptacles 38A and 38B (collectively “receptacles 38”) of connectionmodule 24. Each of leads 16 may carry a plurality of electrodes, and IMD10 may, for example deliver stimulation to the brain of patient 14 viathe electrodes.

Whereas the housing of IMD 10 included a single angled side surface 11that extended substantially circumferentially around IMD 10 tosubstantially define the frustum of a cone, the housing of IMD 30includes a plurality of angled side surfaces 32A-32D (collectively“angled surfaces 32”). Angled surfaces 32 connect top external surface34 to bottom external surface 36. In the illustrated example, bottomexternal surface 36 has a smaller area than top external surface 34.Angled surfaces 32 and top external surface 34 define respective acuteangles 33, one of which is shown for sake of clarity. Similarly, angledsurfaces 32 and bottom external surface 36 define respective obtuseangles 35, one of which is shown for sake of clarity. This configurationallows the IMD to be securely located within a recess in cranium 12,which may have a substantially similar shape to the shape of the housingof IMD 30, for the reasons discussed above with respect to IMD 20.

Acute angles 33 of IMD 30 may be substantially similar to each other,and to the acute angle defined by top external surface 13 and the singleangled side external surface 11 of IMD 10 described with reference toFIG. 1. These acute angles may be less than approximately 65 degrees.Obtuse angles 35 of IMD 30 may be substantially similar to each other,and to the obtuse angle defined by bottom external surface 19 and thesingle angled side external surface 11 of IMD 10 as described withreference to FIG. 1. These obtuse angles may be greater thanapproximately 115 degrees.

Although the respective acute and obtuse angles 33, 35 defined by theorientation of angled surfaces 32 with respect to top surface 34 andbottom surface 36 may be substantially similar, in other embodiments theangles may be different. Further, although illustrated with respect toan embodiment in which each of side surfaces 32 are angled, e.g., definean acute angle with respect to top surface 34, the invention is not solimited. In various embodiments, any one or more of side surfaces 32 maybe angled. Moreover, IMDs according to the invention are not limited tothe substantially rectangular or circular lateral cross-sectional shapesillustrated in FIGS. 1A-2B, and instead may have any ellipsoid,polygonal, or other shape. Whatever cross-sectional shape an IMDaccording to the invention has, the cranial recess may in someembodiments be formed to have a substantially similar shape.

FIGS. 3A-3C are cross-sectional diagrams illustrating IMDs 40A-40C(collectively “IMDs 40”), each including a respective housing 49A-49C(collectively “housings 49”), and a respective member 47A-47C(collectively “members 47”) that at least partially encapsulates thehousing. Each of IMDs 40 includes connection module 24, and isillustrated as implanted within a recess 17 of cranium 12. Accordingly,each of IMDs 40 may have a substantially circular lateral cross-section,similar to IMD 10 of FIG. 1. However, as discussed above, the inventionis not limited to IMDs with any particular cross-sectional shape.

Member 47A covers the upper edge of housing 49A, while member 47B coversthe entire upper surface of housing 49B to provide a transition betweenconnection module 24 and cranium 12. Member 47C covers substantially allof top and side surfaces of housing 49C, and gives IMD 40C an overallshape different from that of housing 49C. Members 47 may provideadvantages with respect cosmesis and skin erosion for IMDs 40 byproviding relatively gradual transitions between edges on housings 49,and between such edges and cranium 12. As illustrated with respect tomembers 47A and 47B, members 47 may extend beyond an outer perimeterdefined by housings 49, and may thereby limit the criticality of thedepth and size of recess 17 by covering the seam between IMDs 40 andcranium 12, e.g., may provide a transition between an upper externalsurface of the IMD and the outer surface of the cranium.

Members 47 may be formed or manufactured from an implantable material,which may be compliant or flexible, such as silicone. Members 47 may beformed using any technique, such as casting or deposition. As anotherexample, members 47 may be machined and later glued or otherwise adheredto housings 49.

Each of IMDs 40 includes a respective one of angled side surfaces42A-42C (collectively “angled surfaces 42”), top surfaces 43A-43C(collectively “top surfaces 43”), and bottom surfaces 44A-44C(collectively “bottom surfaces 44”). For each of IMDs 40, the angledsurface 42 and top surface 43 are oriented to define a respective one ofacute angles 45A-45C (collectively “acute angles 45”), while the angledsurface 42 and bottom surface 44 are oriented to define a respective oneof obtuse angles 46A-46C (collectively “obtuse angles 46”). Acute andobtuse angles 45 and 46 may be substantially similar to each other andacute and obtuse angles 33, 35 discussed above with respect to FIG. 2B.

As illustrated by FIGS. 3A-3C, each of an angled external surface 42,top external surface 43, and bottom external surface 44 may be providedby one or both of a housing 49 or a member 47 that at least partiallyencapsulates the housing. With respect to IMD 40A, for example, themajority of top external surface 43A and substantially the entirety ofangled surface 42A is provided by housing 49A. In contrast,substantially all of top external surface 43B of IMD 40B is provided bymember 47B. Further, substantially all of angled external surface 42Cand top external surface 43C of IMD 40C are provided by member 47C.Member 47C provides IMD 40C, which includes housing 49C with a box-likeshape, a significantly different shape that includes angled surface 42C,as well as acute and obtuse angles 45C and 46C.

FIGS. 4A-4D illustrate techniques for manufacturing an IMD 60. IMD 60may be manufactured by forming respective housing portions 61, 64 for atop assembly 69 and a bottom assembly 71. Housing portions 61, 64 may beformed of any material using any technique, and as an example may beshallow-drawn Titanium shield halves. In the illustrated example, tophousing portion 61 provides an upper external surface for IMD 60, whilethe bottom housing portion 64 provides both angled side and bottomexternal surfaces for the IMD. However, the invention is not so limited.For example, in other embodiments, a top housing portion may provide allor part of an angled side external surface for an IMD. Further, asdiscussed above, such surfaces may alternatively be provided in part orin their entirety by a member that at least partially encapsulates theIMD housing.

As illustrated in FIG. 4A, feedthroughs 67A and 67B (collectively“feedthroughs 67”) are formed through top housing portion 61, and aconnection module 62 is mounted on the top external surface provided bytop housing portion 61. Feedthroughs 67 provide electrical connectionsbetween electrical contacts within receptacles 63A and 63B of connectionmodule 62 and circuitry within the assembled housing of IMD 60.Feedthroughs 67 may be hermetic, as is known in the art. Although twofeedthroughs 67 are illustrated in FIG. 5A, housing portion 61 mayinclude any number of feedthroughs 67, and the number of feedthroughsmay generally correspond to the number of electrodes provided by leads16 coupled to connection module 62.

To reduce the thickness of IMD, printed wiring board (PWB) 65 is formedwithin bottom housing portion 64. PWB 65 may include many of thecomponents of IMD 60, such as digital circuits, e.g., integrated circuitchips and/or a microprocessor, and analog circuit components. Forexample, PWB 65 may be manufactured using FR-4 PWB technology. PWB 65may include a single integrated circuit (IC) and with flip-chiptechnology may be used to place components on PWB 65. Other electricalcomponents may be mounted directly on printed PWB 65 using pick andplace technology, and then secured using reflow of solder.

A flexible tape interconnect 66 may also be connected to PWB 65 with asolder connection. A battery 68 and a telemetry coil 70 may be mountedwithin bottom portion 64 above PWB 65. In other embodiments, telemetrycoil 70 may be formed directly on PWB 65. Battery 68 may a rechargeableor primary battery.

As shown in FIG. 4C, flexible tape interconnect 66 may be connected tofeedthroughs 67. In this manner, leads 16 inserted into receptacles 63may be electrically coupled to the circuitry within IMD 60 via flexibletape interconnect 66. Flexible tape interconnect 66 may be, for example,soldered to feedthroughs 67.

As shown in FIG. 4C, flexible tape interconnect 66 may be connected tofeedthroughs 67 while upper housing portion 61 is located upside-downand adjacent to lower housing portion 64. As can be seen in FIG. 4C, useof flexible tape interconnect 66 may facilitate a relatively easy“side-by-side” assembly of, and electrical coupling between, assemblies69 and 71. Upper portion 61 may then be “folded” onto lower portion 64.A flange 74 of upper portion 61 and flange 72 of lower portion 64 maythen be welded together or otherwise bonded to form a substantiallysealed enclosure for the electrical components of IMD 60.

FIG. 5 is a functional block diagram illustrating electronic componentsof an IMD. Electronic components shown in FIG. 5 are operable to provideneurostimulation or some other stimulation therapy to a patient viastimulation leads 100. For example, FIG. 5 may illustrate electroniccomponents of IMD 60 from FIGS. 4A-4D.

Integrated circuit 80 includes all the components within the dottedline. The remainder of the components may be separately mounted onto aPWB of the IMD. Specifically, integrated circuit 80 includes rechargeblock 80, power management 90, telemetry block 88, processor 92, clock96 and stimulation engine 94. Components not included in integratedcircuit 80, include recharge/telemetry coil 82, Xtal oscillator 84,which allows clock 96 to measure time, rechargeable battery 98,stimulation leads 100 and stimulation capacitors/inductors 102.

FIGS. 6A-6D illustrate exemplary axial cross-section shapes of IMDs. Thecross-section shapes of IMDs shown in FIGS. 6A-6D may be cross-sectionshapes of rectangular, circular or other form-factor IMDs.

The IMDs described with respect to FIGS. 1-5 have shown IMDs havingaxial cross-sections similar to that of shape 120 of FIG. 6A. Shape 120includes convex top surface 126, concave bottom surface 124 and one ormore angled surfaces 125. Concave bottom surface 124 is adjacent to theangled surfaces 125 and non-adjacent to convex top surface 126. Convextop surface 126 is substantially parallel to concave bottom surface 124.Convex top surface 126 and angled surfaces 125 define acute angle 127.Concave bottom surface 124 and angled surfaces 125 define obtuse angle128.

FIG. 6B illustrates another exemplary cross-section shape, shape 130.Shape 130 includes convex top surface 136 and convex bottom surface 134.Convex top surface 136 and convex bottom surface 134 are adjacent, andare oriented to define an acute angle 137.

FIG. 6C illustrates another exemplary cross-section shape, shape 140.Shape 140 includes flat top surface 146, flat bottom surface 144 andangled surfaces 145. Flat top surface 146 is substantially parallel toflat bottom surface 144. Flat top surface 146 and angled surfaces 145define acute angle 147. Flat bottom surface 144 and angled surfaces 145define obtuse angle 148.

FIG. 6D illustrates another exemplary cross-section shape, shape 150.Shape 150 includes convex top surface 156, flat bottom surface 154,angled side surface 155 and substantially perpendicular side surface159. Convex top surface 156 and angled surface 155 define acute angle157. Flat bottom surface 154 and angled surface 155 define obtuse angle158.

FIGS. 7A-7B illustrate tool 160, which may be used to create a cranialrecess shaped to receive an IMD. Tool 160 includes a head 162 with arotating cutting blade 164. Head 162 is located at the distal end ofshaft 167. Handle 166 is located at the proximate end of shaft 167.Trigger 168 is near handle 166 and provides a means selectively operatecutting blades 164.

The profile of cutting blades 164 substantially matches the shape of anIMD to be implanted in the cranium of a patient. For example, the IMDmay have a substantially circular lateral cross-section, like IMD 10 ofFIGS. 1A-1B. A physician operates tool 160 by locating head 162 at aposition on the cranium at which the IMD is to be implanted. The lowprofile of head 162 allows this position to be remote from the handle166. For example, the position may be underneath the scalp of thepatient within a pocket formed next to an incision in the scalp.

The physician then actuates trigger 168 to turn-on cutting blades 164.Optionally, trigger 168 may be pressure-sensitive so that the physiciancan control the speed of cutting blades 164. Cutting blades 164 may bepowered by an electric motor located within head 162 or otherwiselocated. In other embodiments, cutting blades 164 may be poweredpneumatically. Once the physician turns on cutting blades 164, thephysician may apply downward pressure on head 162. For example, thephysician may apply downward pressure on head 162 through the scalp ofthe patent.

The physician is finished creating the cranial recess once surface 163reaches the cranium. In this manner, surface 163 ensures that thephysician can not remove too much bone from the cranium. Whilepreferably the physician would not breach the inner table of the craniumwith tool 160, tool 160 may include an automatic shut-off in case thetool loses resistance. Even if the inner table of the cranium isbreached, the recess may still hold an IMD, because the top portion ofthe IMD is larger than the bottom portion of the IMD. The automaticshut-off may also operate once surface 163 reaches the cranium becausecutting blades 164 may also lose resistance in this situation.

Tool 160 may also include a suction mechanism (not shown) in head 162 toremove pieces of bone and other cranial matter created during theoperation of tool 160. In other embodiments, a physician may use aseparate suction tool to remove pieces of bone and other cranial mattercreated by the operation of tool 160.

Various embodiments of the invention have been described. However,various modifications may be made to the described embodiments withinthe spirit of the invention. For example, embodiments of the inventionare generally described with respect to an IMD having a housing with atop surface and a bottom surface connected by an angled surface. In someembodiments, an IMD housing may include as few as two surfaces joined ata single edge. In such embodiments, at least one of these surfaces maybe convex to make room for components within the housing. Other shapesfor IMDs are also possible.

Further, although described above with reference to cranial recessesthat have a substantially similar shape to an IMD, the invention is notso limited. For example, in some embodiments, a cranial recess may beformed with substantially perpendicular side walls, or side walls thatare in any event more perpendicular than the angled surfaces of the IMD.In such embodiments, the cross-sectional area of the top of the recessmay larger than the cross-sectional area of the bottom of the IMD, e.g.,so that the IMD may be more easily placed in the recess from an incisionremotely located from the recess, as discussed above. Cross-sectionalareas of the tops of the recess and IMD may be substantially similar.These and other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A tissue stimulation system, comprising: at leastone implantable neurostimulation lead; and an implantableneurostimulator comprising a header having at least one connectorassembly configured for respectively receiving the at least oneneurostimulation lead, a circuit board having programming circuitry, aflex circuit coupled between the at least one connector assembly and thecircuit board, and a case to which the header is coupled, the caseincluding a hermetically sealed compartment enclosing the circuit boardand the flex circuit.
 2. The tissue stimulation system of claim 1,wherein the flex circuit is coupled to the circuit board by soldering.3. The tissue stimulation system of claim 1, further comprising afeedthrough assembly coupled between the flex circuit and the at leastone connector assembly, the feedthrough assembly comprising a pluralityof pins coupled to the flex circuit that electrically couple the flexcircuit to the at least one connector assembly.
 4. The tissuestimulation system of claim 3, wherein the at least one connectorassembly comprises a plurality of connector contacts for electricallycoupling with the neurostimulation lead, and the pins are electricallycoupled to the connector contacts.
 5. The tissue stimulation system ofclaim 1, wherein the at least one connector assembly comprises aplurality of connector contacts.
 6. An implantable neurostimulator,comprising: at least one connector assembly configured for receiving atleast one neurostimulation lead; a circuit board having programmingcircuitry; a flex circuit coupled between the at least one connectorassembly and the circuit board; and a case including a hermeticallysealed compartment containing the circuit board and the flex circuit. 7.The neurostimulator claim 6, wherein the flex circuit is coupled to thecircuit board by soldering.
 8. The neurostimulator of claim 6, furthercomprising a feedthrough assembly coupled between the flex circuit andthe at least one connector assembly, the feedthrough assembly comprisinga plurality of pins coupled to the flex circuit that electrically couplethe flex circuit to the at least one connector assembly.
 9. Theneurostimulator of claim 8, wherein the at least one connector assemblycomprises a plurality of connector contacts, and the pins areelectrically coupled to the connector contacts.
 10. The neurostimulatorof claim 6, wherein the at least one connector assembly comprises aplurality of connector contacts.
 11. The neurostimulator of claim 6,further comprising a shell containing the at least one connectorassembly.
 12. The neurostimulator of claim 6, further comprising aheader containing the at least one connector assembly, wherein theheader is coupled to the case.